318 
CAPTAIN L. DARWIN, DR. A. SCHUSTER, AND MR. E. W. MAUNDER 
no good results are to be expected. As to whether the experiment should be 
repeated, it is to be oljserved that the coronagrapb is admirably adapted for taking 
photographs of the corona during totality, for ordinary records ; for reflectors have 
several advantages over refractors for this purpose, and the special contrivances of 
this instrument would all be more or less useful under the circumstances. Hence, 
another trial can easily be combined with what may be described as the ordinary 
routine work of an eclipse. Atmospheric or other conditions are now certainly 
unfavourable, and time only can settle the question whether this is a permanent or a 
temporary difiiculty."^ I should therefore recommend the experiment being made 
again in connection with other work, but not before the next occasion when the path 
of a total eclipse passes over high ground (say, over 7000 feet) which can be con¬ 
veniently reached, and where there appears to be a reasonable chance of having a 
clear atmosphere. But on all occasions it would, I think, be worth while arranging 
that some one, not necessarily a trained astronomer, should be detailed to observe for 
how long before and after totality the outer limb of the Moon can be observ^ed. 
This was not done at Grenada. During partial eclipses a look-out should also be 
kept for this phenomenon. 
Most of what I have said has been unfavourable to Dr. Huggins’ method. But 
there is very material evidence in its favour, and, for the benefit of any one reading 
up this subject, I have given the necessary references in a footnote.t 
VII. The Prismatic Camera. By Captain Darwin. 
1. Description and Adjustments. 
The instrument was the same as that used by Dr. Schuster, in Egypt, in 1882 
(see ‘Phil. Trans.’ 1884, Part I.), and by Mr. Lawrance, at Caroline Island (‘Phil. 
Trans.,’ A, 1889). 
The camera has a lens of 3 inches aperture, and of 20 inches focal length. There 
is no slit, and the prism, which is placed directly in front of the lens, has a refracting 
angle of 60°. A photograph taken with this instrument of any small object which 
has a bright line spectrum will shew several images, each one corresponding to some 
* It is a curious fact, that the limb of the Moon beyond the Sun has seldom been reported to have 
been observed long before totality during the last 15 years, although before that date it is said to have 
been seen on sevei’al occasions. See ‘ Astron. Soc. Mem.,’ vol. 41, 1879, pp. 25-39. 
t (I.) “ On a Method of Photographing the Solar Corona without an Eclipse.” W. HuGGixs, 
‘ Roy. Soc. Proc.,’ No. 223, 1882. 
(2.) “ On some Results of Photographing the Solar Corona without an Eclipse.” W. HuGGixs, 
‘ Brit. Assoc. Rep.,’ 1883. 
(3.) “ On the Coroua of the Sun.”—Bakerian Lecture for 1885. W. Huggins, ‘ Roy. Soc. Proc.,’ 
No. 239, 1885. 
(4.) “ Photographing the Corona without an Eclipse.” E. L. Tronveldt, ‘ Observatory,’ No. 117 
1886 
